1. Field of the Invention
The invention relates to methods of capping poly(phenylene ether) resin, and more particularly relates to methods of capping poly(phenylene ether) resin having an intrinsic viscosity between 0.05 and 0.35 dl/g, preferably between about 0.09 and 0.15 dl/g.
2. Brief Description of the Related Art
Poly(phenylene ether) resins (referred to hereafter as "PPE") are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Commercially, most PPE are sold as blends with predominantly high impact polystyrene resins. PPE are miscible with polystyrene resins in all proportions and because of the very high glass transition temperatures of PPE, the blends of PPE with polystyrene resins possess higher heat resistance than that of the polystyrene resins alone. Examples of such blends can be found in U.S. Pat. Nos. 3,383,435; 4,097,550; 4,113,800; 4,101,503, 4,101,504; 4,101,505; 4,128,602; 4,139,574; and 4,154,712 among others.
Many commercial poly(phenylene ether) resins posses end groups having an aromatic hydroxyl moiety, generally an alkyl substituted phenol residue. These residues are believed to act as radical scavengers and consequently limit the utility of poly(phenylene ether) resins in applications involving desirable radical reactions. One example of a desirable application is the polymerization of styrene monomer, either alone or with comonomers, in the presence of poly(phenylene ether) resin. Similarly, poly(phenylene ether) resins become dark and embrittled in the presence of oxygen and high temperatures, presumably due to oxidation of these same hydroxyl groups. Capping the hydroxyl moieties present in PPE affords a solution to many of these problems. Moreover, capped PPE would also have utility in many PPE blends such as, for example, blends with other thermoplastic polymers as well as thermoset resins including unsaturated polyurethane resins, allylics, bismaleimides, and the like.
U.S. Pat. No. 4,760,118 describes a method to cap poly(phenylene ether) resins in a melt (i.e. solventless) process. The method described in the aforementioned patent was exemplified using a poly(phenylene ether) resin having an intrinsic viscosity of about 0.48 dl/g and afforded solutions to issues for capping relatively high molecular weight poly(phenylene ether) resin.
Recently, interest has increased in poly(phenylene ether) resins having an intrinsic viscosity between 0.05 and 0.35 dl/g due, in part, to their increased processability and miscibility as compared to commercially available resins having intrinsic viscosities between 0.40 and 0.49 dl/g. With the reduced intrinsic viscosity the number of endgroups increases and aforementioned problems become accentuated.
Capping poly(phenylene ether) resin relatively low molecular weight poly(phenylene ether) resin, e.g., having an intrinsic viscosity between 0.05 and 0.35 dl/g, presents issues that were not previously recognized. For example, relatively low molecular weight poly(phenylene ether) resin has a significantly higher proportion of hydroxyl moieties for capping. Similarly, relatively low molecular weight poly(phenylene ether) resin can not be efficiently isolated after polymerization using conventional solvent precipitation techniques due to the extremely small particle size generated with conventional techniques. The low melt strength of relatively low molecular weight poly(phenylene ether) resin also presents special issues, especially with stranding and chopping the extrudate.
It is therefore apparent that there continues to be a need for improved methods for capping relatively low molecular weight poly(phenylene ether) resin.